It has been known to use overlay welding techniques in cylinders such as to improve the bore wear characteristics. Thus, in U.S. Pat. No. 2,292,662 it has been taught to weld spray a cylinder bore with a hard-wearing metal or alloy such as a chromium alloy. After such operation the bore can be machined to prepare a smooth surface. In a somewhat related teaching, U.S. Pat. No. 3,019,327 shows fusion welding of an overlay of clad metal onto a base metal. This technique is taught as useful in fabricating reactor shells, steam generators and other high temperature pressure vessels.
Other methods have also been employed to obtain water-resistant parts. Thus, in U.S. Pat. No. 3,980,506 there has been shown the use of a roller polishing operation together with a surface hardening operation which may be carburizing or nitriding. Furthermore, special applications can require special techniques. For example, U.S. Pat. No. 4,256,518 focuses on the outer periphery of a transition piece of a box tool joint member. This patent teaches first forming an annular groove in the outer periphery. Then a butter layer is welded into the groove and heat treated. Lastly, a hard facing layer is added to the butter layer.
Considering again the problem of wear resistance for interior surfaces, U.S. Pat. No. 3,918,137 focuses on preparing a wear-resistant surface for an internal combustion engine. To accomplish this, there is first thermally sprayed a coating of particles which are of generally equal hardness such as particles of a martensitic stainless steel mixed with a particulate hard nickel based alloy. The sprayed coating is immediately quenched in oil. Thereafter it is machined to a finished contour. In further regard to internal combustion engines, wear resistance for rocker arms has also attracted attention. In U.S. Pat. No. 3,827,920 an atomized molten metal, more particularly a self-fluxing alloy is sprayed onto the substrate metal surface. The applied metal is thereafter fused. Lastly, it is subjected to a nitriding or carbonitriding treatment.
Pump liners also require high hardness to provide suitable service. In current practice, the solution for providing this hard liner surface has most typically been the use of a high chrome iron sleeve. The high chrome iron sleeve can be centrifugally cast. After annealing to reduce the hardness to a machineable range, the casting may be bored and turned. The sleeve is then hardened by heating and air cooling. Afterwards it is ground to the inside diameter of the shell and assembled into the shell by shrink fitting. But maintenance of the fitting in place can be a problem.
Accordingly, it is the principal object of the present invention to provide a means of overcoming typical problems associated with the various prior art techniques for hardening the wear surface of a given article, such as a pump liner.
In addition, other objects of the present invention will become apparent to those skilled in the art from a reading of the following specification and claims.